Study On Protein Oxidation And Functional Characteristics Of Selenium-rich Rice During Storage Based On Proteomics

Selenium enriched rice is an effective way to supplement selenium.Due to the characteristics of production and consumption,rice is prone to aging due to external environmental factors and internal grain metabolism during long-term storage.Lipid oxidation in rice produces peroxides,primary/secondary metabolites and free radicals which can attack proteins and induce structural and functional changes of proteins.Therefore,it is of great significance to study the oxidation law and interaction between lipid and protein,protein quality change and protein metabolism pathway of rice during storage.In this paper,the oxidation and structural changes of lipid and protein in ordinary rice and selenium-rich rice were studied after 180 days of storage at different temperatures(15 °C,25 °C and 35 °C).Rice crude oil-lipoxidase(LOX)-rice protein was used to simulate the oxidation of lipids and proteins during storage to clarify the quality degradation mechanism of rice storage.On this basis,the differential proteins(DEPs)of rice under different storage conditions were identified based on proteomics technology,and the metabolic pathways involved in rice storage were identified.The conclusion is as follows:(1)The lipid and protein quality changes of rice stored at different temperatures for 180 days were studied.The results showed that storage temperature and storage time had significant effects on lipid and protein oxidation of the two kinds of rice.With the increase of storage time,the contents of fatty acid,carbonyl group and free sulfhydryl group increased,disulfide bond content decreased,peroxide value and malondialdehyde content first increased and then decreased.It was found that high temperature can promote lipid oxidation process.Lipid oxidation and protein oxidation degree of rice at high temperature were higher.The lipid and protein oxidation stability of selenium-enriched rice in storage is stronger than that of ordinary rice.(2)The protein structure changes of rice stored at different temperatures for 180 days were characterized.The results showed that the protein composition and structure changed after storage.The content of essential amino acids of rice protein decreased at different temperatures.The secondary structure changes from ordered structure to disordered structure.The composition of protein subunits did not change significantly,and the content of high molecular weight subunits decreased.Protein surface hydrophobicity increases,particle size increases,and surface smoothness decreases.Tryptophan was attacked by oxidation and the endogenous fluorescence absorption intensity decreased.This indicated that rice protein was oxidized during storage,some amino acid residues were oxidized during storage,hydrophobic groups inside the protein were exposed,and the structure of the protein gradually extended and changed.(3)The oxidation system of rice crude oil-LOX-protein was constructed to simulate the lipid oxidation and protein oxidation process in rice storage.The results showed that lipid oxidation induced protein oxidation and structural changes.With the increase of lipid oxidation degree,the carbonyl value of the two rice gluten increased;the free sulfhydryl content is reduced,the secondary structure composition was transformed into each other,the average particle size and surface hydrophobicity increased,the endogenous fluorescence intensity decreased,the maximum absorption peak red shift,the surface smoothness decreased,and the conformation of rice proteins underwent complex changes.(4)The DEPs of the two kinds of rice before and after storage at different temperatures were identified.Combined with the gene ontology(GO)and the Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis,the deterioration mechanism and metabolic differences of the two kinds of rice were expounded.A total of 2992 trusted proteins were identified.GO analysis showed that DEPs were mainly concentrated in secondary items such as enzyme activity regulation,molecular function regulation,organelle component changes,nutrient storage activities and immunoglobulin binding.KEGG analysis showed that DEPs were mainly concentrated in the metabolic pathways related to starch and sucrose metabolism,pyruvate metabolism,fatty acid generation and degradation,and sulfur metabolism.Compared with 15 °C,rice at 35 °C produced more reductive protease to cope with high temperature oxidative stress.Under the same storage conditions,the expression level of antioxidant-related metabolic pathways in selenium-enriched rice is higher than that in ordinary rice.